The use of composite structures is increasingly common on commercial aircraft. As heralded by the newest generation of commercial aircraft, composites may soon become the predominant material. Composites may be damaged in the course of service. Examples of such in-service damage include impact damage due to hail, runway debris (foreign object damage), or collisions with ground support vehicles.
Referring to FIGS. 1A-1C, the damage may be categorized, for example, as a low energy impact with slight damage (FIG. 1A) or possibly corrosion, a low energy impact with moderate damage (FIG. 1B), or a medium energy impact with severe damage (FIG. 1C). As shown in FIGS. 1A-1C, visual detection may not be an accurate indicator of the degree of damage. Because of the complex structure of composite materials, however, permanent repair methods can be quite involved and are normally undertaken only at appropriate maintenance facilities.
A problem remains as to a course of action when damage is discovered. For example, damage may be discovered at the airport loading gate just prior to a departure. If repair equipment is not available or if the repair may be extensive, the flight might be cancelled. The aircraft may be grounded and taken out of service to be ferried or towed to a maintenance base, with consequent significant economic impact to the aircraft operator.
A “temporary structural repair” may be provided that would restore the damaged area (e.g., applied over the damage instead of removing the damage), to restore the damaged structure to an acceptable strength, until the next major maintenance visit. However, the extent of the damage may need to be determined even as passengers are waiting at the boarding gate, expecting to depart. Without knowledge of the extent of damage, one cannot determine if a temporary repair may restore the structure. For example, if the damage is determined to be superficial, the aircraft may be released for departure.
There are various configurations of composite structural components, and often the method of inspection for each may be quite different. Audible tap testing, considered sufficient to determine sub-surface damage in thin-skinned honeycomb sandwich structures, may be inadequate to evaluate large honeycomb sandwich elements with thick face sheets, such as flaps, landing gear doors, and raked wing tips. Thick solid laminate structures may be common to the majority of the external surface of newer aircraft. A heavy impact may not show significant visually discernable surface damage, but severe hidden delamination and cracking within the structure may have occurred. Thus, various damage repair scenarios must be considered where the damage at a damage site may be difficult or impossible to detect visually (e.g., as illustrated in FIGS. 1A-1C).
Sub-surface inspection of complex composite structures may require sophisticated nondestructive inspection (NDI) devices. However, a trained NDI technician may not be available at the many locations where apparent damage on a structure may be detected. Hence, there remains a need in the art for providing improved NDI services.